JPH06268237A - Semiconductor acceleration sensor - Google Patents

Abstract

PURPOSE:To enable the self-excitation power of a semiconductor acceleration sensor to be accurately applied even if sensors vary in gap length by a method wherein the sensor is made to make a self-diagnosis by applying a voltage between an overlap and an electrode. CONSTITUTION:A <100> plane of Si is formed into an overlap 3 and a beam 2 which supports the overlap 3 through ECE, and a semiconductor acceleration sensor board is equipped with a support 1 which is so formed as to surround the overlap 3 and the beam 2, wherein piezoelectric resistors 6 are provided to the upside of the beam 2. An Si base 5 is bonded to the undersides of the support 1 and the overlap 3. Recesses 8 and 14 equal to each other in depth are provided to the Si base 5. A capacitor is composed of the underside of a sensor P-type substrate and an electrode 15 in the recess 14 to serve as an electrostatic capacity monitor. A driver is driven by an electrostatic drive voltage value obtained basing on the capacity of the capacity monitor, and the drive voltage is applied to an electrode 13 and the P-type substrate of the overlap 3. By this setup, a self-excitation takes place precisely. A sensor out of sensitivity alignment can be calibrated basing on a sensitivity output at self- diagnosis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic drive type semiconductor acceleration sensor having a self-diagnosis function.

[0002]

2. Description of the Related Art A conventional semiconductor acceleration sensor will be described with reference to FIG. The semiconductor acceleration sensor shown in the figure is a cross-sectional view of a doubly supported beam type semiconductor acceleration sensor having an electrostatic drive type self-diagnosis function.
e Bruin, Henry V. Allen, "Self-testable Accelerometer
Microsystem ", Micro System Technologies '90, Berli
n, Germany, pp. 611-616 (1990).

In FIG. 4, reference numeral 1 denotes a silicon substrate of a sensor chip, on which a thin beam 2 is formed by anisotropic etching from the back surface, which is a so-called double-supported beam which indicates a central weight portion 3 from both sides. It has a structure. A silicon cap 4 having a recess 7 is adhered to the upper surface of the silicon substrate 1 and a silicon pedestal 5 having a recess 8 is adhered to the lower surface by alloy bonding or the like, and the weight portion 3 is vertically moved according to acceleration. The structure allows displacement, and the displacement is limited by the projections 9 and 10 in the recesses 7 and 8 to prevent damage to the beam when excessive acceleration is applied.

A piezoresistor 6 is formed on the surface of the beam 2, and when the weight portion 3 is displaced by the application of acceleration and stress is generated on the surface of the beam, the resistance value changes and the acceleration can be detected. ing. Here, the piezoresistors 6 are formed on the pointing portion side and the weight portion side of the beam, and a full bridge (not shown) is configured by utilizing the fact that the stresses have opposite polarities.

The narrow gap formed by the cap 4 and the pedestal 5 not only functions as a stopper for the weight portion 3, but also enables air damping for suppressing resonance of the beam.

A metal electrode 1 for self-diagnosis is provided on the weight portion 3.
1 is formed and faces the upper cap 4 across a narrow gap. A metal electrode (not shown) is also formed in the concave portion of the cap 4, and this electrode is electrically connected to the metal electrode (not shown) on the silicon substrate 1 at the bonding portion and is drawn out to the bonding pad 12. There is.

When a voltage is applied between the electrode of the upper cap 4 and the electrode 11 on the weight portion 3, the weight portion 3 is displaced upward by an electrostatic force, and the same stress as when acceleration is applied is generated in the beam. be able to. By checking the output at this time, so-called self-diagnosis, which confirms the detection function of the sensor, becomes possible.

Here, the excitation force F due to electrostatic drive is given by the following equation. F = εS (V / d) 2/2 ε: dielectric constant, S: area, d: Therefore gap length, the voltage applied between the electrodes in order to obtain the excitation force F is as follows. V = d (2F / εS) ^1/2 (1)

[0009]

However, in the electrostatic drive type self-diagnosis in such a conventional semiconductor acceleration sensor, in order to obtain the self-exciting force F, V = d ( Since the voltage V of 2F / εS) ^1/2 is applied, it is difficult to control the gap length d and it is difficult to accurately apply the self-exciting force F due to variations in d between the sensors. There was a problem.

Therefore, the present invention has been made in view of the above conventional circumstances, and an object thereof is to accurately apply the self-exciting force even if the gap length varies among the sensors. It is to provide a semiconductor acceleration sensor capable of performing the above.

[0011]

In order to achieve the above object, the present invention provides a weight portion formed of a semiconductor substrate,
A support portion that surrounds the weight portion, a thin beam portion or a plurality of thin beam portions that connect the weight portion to the support portion, and a lower surface of the support portion that are adhered to each other and have equal depths below the weight portion and below the support portion. The pedestal having the groove and the groove below the supporting portion are grooves for capacitance monitoring, and detection means for measuring the capacitance of the capacitance monitoring groove and electrostatic capacitance from the output of the detection means. The beam portion includes an arithmetic means for obtaining a driving voltage and a driving means for electrostatically driving by generating the voltage value obtained by the arithmetic means, and the beam portion with respect to an acceleration in a direction perpendicular to the surface of the weight portion. Acceleration can be detected by a change in the resistance value of the piezoresistor formed on the beam portion, and self-diagnosis can be performed by applying a voltage between the weight portion and an electrode formed on the groove below the weight portion. It is characterized by doing.

[0012]

In the above structure, according to the present invention, the capacitance monitor is provided in the sensor to detect the capacitance, and the driver is driven by the arithmetic processing. Therefore, the variation in the gap length of each sensor is not affected. , The self-exciting force can be applied accurately.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the configuration of an embodiment according to the present invention.

In FIG. 1, in this semiconductor acceleration sensor, a Si <100> surface is formed with a weight portion 3 and a beam portion 2 supporting the weight portion by ECE (electrochemical etching), and a supporting portion having a shape surrounding them. 1 is a semiconductor acceleration sensor substrate having a piezoresistor 6 formed on the beam 2.

Si is provided below the supporting portion 1 and the weight portion 3.
The pedestal 5 is bonded, and the Si pedestal 5 has recesses 8 and 14 of the same depth formed by etching.
Metal electrodes 13 and 15 are formed in the recesses 8 and 14 by vapor deposition and patterning.

FIG. 2 is a block diagram of the electrostatic drive circuit. The concave portion 14 forms a capacitor by the lower surface of the sensor P-type substrate and the electrode 15, and this is a capacitance monitor 16. A capacitance detection circuit 17 is connected to the capacitance monitor 16, and its output is connected to an arithmetic circuit 18. The output of the arithmetic circuit 18 is connected to the driver 19, and the output of the driver 19 is connected to the electrode 13 and the weight portion 3.

Next, the operation of the semiconductor acceleration sensor thus constructed will be described. When acceleration in the direction perpendicular to the substrate surface is applied to the acceleration sensor substrate, the weight portion 3 is displaced accordingly and the beam portion 2 is bent. At this time, stress is generated on the surface of the beam portion 2, and the resistance value of the piezoresistor 6 formed on the beam portion 2 changes according to this stress.

The acceleration can be detected by forming a full bridge with the piezoresistors 6 on the beam portion 2 and measuring the change in the resistance value of the bridge. The sensor substrate has an n-epi layer on the surface of a P-type substrate, and when a voltage is applied between the P-type substrate and the electrode 13 via P ^{+ of the} n-epi layer, a static electricity is generated between the lower part of the weight part 3 and the electrode 13. Electric power is generated, the weight portion 3 is displaced downward, and the same stress as when acceleration is applied can be generated in the beam. By checking the output at this time, self-diagnosis of the detection function of the sensor is possible.

A recess 14 for capacitance monitoring is formed on the pedestal, and the gap length between the electrode 15 and the lower surface of the supporting portion 1 is formed to be equal to the gap length between the electrode 13 and the lower surface of the weight portion 3. There is. Further, assuming that the lower area of the weight portion 3 is S and the area of the electrode 15 is S ′, and the relation of S = nS ′ is established, the electrostatic capacitance C of the electrostatic capacitance monitor is as follows.

C = εS ′ / d = εS / nd (2) When this equation (2) is substituted into the above equation (1), the following equation is obtained.

V = (2εSF) ^1/2 / nC (3) Therefore, by measuring the capacitance C between the P-type substrate of the sensor substrate and the electrode 15, the electrostatic drive voltage V can be calculated from the equation (3). It can be determined and is not affected by variations in gap length.

Further, in the equation (3), since k can be regarded as a constant as V = k / C (k = (2εSF) ^1/2 / n (4)), C can be detected by detecting C It is possible to automatically determine the electric drive voltage.

In the configuration of FIG. 2, the capacitance detection circuit 17 detects the capacitance of the capacitance monitor 16 and the arithmetic circuit 18 obtains the value of the electrostatic drive voltage. With this value, an electrostatic drive voltage is generated in the driver 19, and this voltage is supplied to the electrode 13 and the P-type substrate of the weight portion 3.

This voltage is applied between the electrode 13 and the lower surface of the weight portion 3, and self-excitation can be performed with high precision. Further, it is possible to calibrate the sensitivity deviation such as a change with time based on the sensitivity output at the time of self-diagnosis.

FIG. 3 shows a specific example of the electrostatic drive circuit. As shown in this figure, the electrostatic drive circuit first detects the capacitance monitor 16,
An oscillating circuit including a resistor 20 and a Schmitt trigger 21 is configured, and a one-shot circuit 22 and an integrating circuit 2 are provided ahead of this.
3. The amplifier circuit 24 is connected to output the electrostatic drive voltage V _in .

The oscillation circuit consisting of the capacitance monitor 16, the resistor 20 and the Schmitt trigger 21 is f coupled by CR coupling.
= A / (2πCR), where a is a constant, and the Schmitt trigger 21 outputs a step pulse clock voltage. After passing this output through the one-shot circuit 22, the integration circuit 23 integrates
A voltage V _d proportional to the frequency f is obtained. This voltage V _d is C
Since it is inversely proportional to, the electrostatic drive voltage V _in = k / C can be obtained by amplifying V _d .

[0027]

As described above, according to the present invention, as the electrostatic drive self-diagnosis function, the electrostatic capacity monitor is provided in the sensor to detect the electrostatic capacity, and the driver is driven by the arithmetic processing from the electrostatic capacity. Since the voltage is determined, the self-exciting force can be accurately applied without being affected by the variation in the gap length of each sensor, and the exciting force can be automatically determined.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of an embodiment relating to a semiconductor acceleration sensor of the present invention.

FIG. 2 is a configuration diagram of an electrostatic drive circuit according to an embodiment of the semiconductor acceleration sensor of the present invention.

FIG. 3 is a specific example of the electrostatic drive circuit shown in FIG.

FIG. 4 is a sectional view showing a configuration of a conventional semiconductor acceleration sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Support part 2 Beam part 3 Weight part 4 Silicon cap 5 Silicon pedestal 6 Piezoresistive 7,8 Recessed part 9,10 Projection part 11,13 Metal electrode 12 Bonding pad 14 Capacitance monitor (recessed part) 15 Capacitance monitor (metal) Electrode) 16 Capacitance monitor 17 Capacitance detection circuit 18 Arithmetic circuit 19 Driver circuit 20 Resistance 21 Schmitt trigger 22 One shot circuit 23 Integration circuit 24 Amplification circuit

Claims (1)

[Claims] 1. A weight portion formed from a semiconductor substrate, a support portion surrounding the weight portion, a thin beam portion or a plurality of thin beam portions connecting the weight portion to the support portion, and an adhesive to a lower surface of the support portion. A pedestal having grooves of equal depth below the weight portion and below the support portion, and the groove below the support portion is a groove for capacitance monitoring, and the capacitance of the groove for capacitance monitoring is And a driving means for electrostatically driving by generating a voltage value calculated by the calculating means, and a detecting means for measuring an electrostatic drive voltage from an output of the detecting means. The beam portion bends with respect to the acceleration in the direction perpendicular to the surface of the, and the acceleration can be detected by the change in the resistance value of the piezoresistor formed on the beam portion. By applying a voltage between the formed electrodes The semiconductor acceleration sensor and performing a self-diagnosis.